1. Field of the Invention
The present invention relates to a keyboard to be employed in giving signals to an electronic apparatus or the like.
2. Description of the Related Art
Keyboards are used widely as input devices for operating personal computers, word processors and the like. A conventional keyboard will be described with reference to FIGS. 10 to 14. Referring to FIGS. 10 to 12, the keyboard has a support plate 1 of a metal having a curved portion 1a, a bent portion 1c and a flat portion 1b, a membrane switch sheet 2 having an upper membrane provided with electrodes, and a lower membrane closely spaced from the upper membrane and provided with electrodes, local portions of the upper membrane being depressed to bring the electrodes thereof to be in contact with the corresponding electrodes of the lower membrane for switching operation, keys 4, a rubber sheet 3 for absorbing shocks applied to the keys 4 by operator' fingertips, and a housing 5 of a synthetic resin having an upper surface on which the keys 4 are arranged. The support plate 1, the membrane switch sheet 2, the rubber sheet 3 and the housing 5 are stacked in that order. Those members excluding the support plate 1, i.e., the membrane switch sheet 2, the rubber sheet 3 and the housing 5, have moderate flexibility that enables those members to curve along the curved portion 1a of the support plate 1.
The keys 4 arranged on the upper surface of the housing 5 are supported by key support mechanisms 5a on the housing 5, respectively, so as to be vertically movable when depressed.
Fastening projections 5b project from predetermined positions on the lower surface of the housing 5. As shown in FIGS. 11 and 12, the membrane switch sheet 2 and the rubber sheet 3 are stacked in that order on the support plate 1 having the curved portion 1a, the bent portion 1c and the flat portion 1b. The housing 5 is placed on the rubber sheet 3 so that the projections 5b are inserted through aligned holes formed in the rubber sheet 3, the membrane switch sheet 2 and the support plate 1. End portions of the projections 5b project from the lower surface of the support plate 1. The end portions of the projections 5b are upset to form a stacked functional structure 6 consisting of the support plate 1, the membrane switch sheet 2, the rubber sheet 3 and the housing 5. In this stacked functional structure 6, the membrane switch sheet 2, the rubber sheet 3 and the housing 5 are curved so as to conform to the shape of the support plate 1 having the curved portion 1a and the flat portion 1b.
In the keyboard provided with the stacked functional structure 6, the curved portion 1a of the support plate 1 is seated on the upper surface of the bottom wall 9a of a lower case 9 and a rib 9b formed on the bottom wall 9a. The flat portion 1b is seated on ribs 9c formed on the bottom wall 9a of the lower case 9 as shown in FIG. 10. The stacked functional structure 6 is located on the lower case 9 by projections, not shown, formed on the lower case 9 and engaging with positioning recesses 1d (FIG. 14) formed in the support plate 1. An upper case 8 is put on the lower case 9, thus supporting the stacked functional structure 6 so that the keys 4 project outside through holes formed in the upper case 8. The upper case 8 and the lower case 9 sandwiching the stacked functional structure 6 therebetween are fastened together with screws, not shown, to complete the keyboard.
As shown in FIGS. 10 to 12, an alphanumeric key unit A is disposed on the upper surface of the housing 5 with the keys 4 included in the alphanumeric key unit A arranged in a curved arrangement along the curved portion 1a of the support plate 1, and a function key unit B is disposed on the upper surface of the housing 5 with the keys 4 included in the function key unit B arranged in a flat arrangement along the flat portion 1b of the support plate 1. Since the rear end of the curved portion 1a of the support plate 1 is seated on the rib 9b, the alphanumeric key unit A rises gradually along the curved portion 1a of the support plate 1 toward the rear. Since the function key unit B is disposed behind the alphanumeric key unit A (on the right-had side, in FIG. 10), as viewed from the operator's side and the flat portion 1b of the support plate 1 corresponding to the function key unit B are supported on the ribs 9c, the function key unit B is disposed in a substantially horizontal position on a level higher than that of the alphanumeric key unit A.
In the conventional keyboard illustrated in FIGS. 10 to 14, the membrane switch sheet 2 and the rubber sheet 3 are stacked on the upper surface of the support plate 1 and holes 1e through which the projections 5b are inserted are formed in the support plate 1, the membrane switch sheet and the rubber sheet 3 (only the holes 1e formed in the support plate 1 are shown) at positions corresponding to the projections 5b of the housing 1. The stacked functional structure 6 is fabricated by inserting the projections 5b through the holes 1e and upsetting the end portions of the projections 5b projecting from the lower surface of the support plate 1 to hold the membrane switch sheet 2 and the rubbers sheet 3 between the support plate 1 and the housing 5.
Although the support plate 1 has the curved portion 1a and the flat portion 1b respectively having different shapes on the opposite sides of the bent portion 1c, the housing 5 formed of a flexible synthetic resin is bent substantially along the bent portion 1c of the support plate 1 and substantially conforms to the shape of the support plate 1 when the stacked functional structure 6 is completed. The housing 5 has a linear bending portion 5d corresponding to the bent portion 1c of the support plate 1 and is capable of being bent along the bending portion 5d when fastened to the support plate 1.
As shown in FIG. 13, housing 5 is fastened to the support plate 1 with its first portion A1, in which the alphanumeric key unit A is disposed, in conformance to the curved portion 1a and its second portion B1, in which the function key unit B is disposed, in conformance to the flat portion 1b. The keys 4 which are more frequently used among those of the alphanumeric key unit A, corresponding to the curved portion 1a of the support plate 1, are arranged at positions nearer to the operator in the curved first portion A1 than those which are less frequently used to facilitate operator's operation for operating the keys and to reduce load on the operator. The keys 4 of the function key unit B, which are less frequently used than the alphanumeric keys 4, are disposed in the flat second portion B1 remote from the operator to form the keyboard in a small thickness.
The support plate 1 having the curved portion 1a and the flat portion 1b of the conventional keyboard thus constructed is formed by processing a large metal sheet by a pressing process or a roll-bending process. The yield of such a process is low and hence the cost of the support plate 1 manufactured by such a process is high.
It is very difficult to form the support plate 1 having the curved portion 1a and the flat portion 1b on the opposite sides of the bent portion 1c in a high accuracy by a press or a bending roll because of the springback of the metal sheet. If the support plate 1 is not formed accurately is design dimensions, the stacked functional structure 6 cannot stably be seated on the bottom wall 9a and the ribs 9b and 9c of the lower case 9 and rattles, which makes work for assembling the keyboard difficult.
The stacked functional structure 6 is constructed by stacking the membrane switch sheet 2 and the rubber sheet 3 on the support plate 1, the housing is put on the rubber sheet 3 so that the projections 5b are inserted through the holes formed in the support plate 1, the membrane switch sheet 2 and the rubber sheet 3, and the end portions of the projections 5b are upset. Since the number of the projections 5b is relatively large, it is very difficult to upset all the fastening projections 5b uniformly so that the curved portion 5a and the flat portion 5b of the housing 5 are fastened equally to the support plate 1. Furthermore, an expensive, large upsetting machine is necessary to upset the fastening projections 5b so that the curved portion 5a and the flat portion 5b are fastened equally to the support plate 1. Such problems may be solved by individually upsetting the plurality of fastening projections 5b on at a time, which, however, takes much time.